Subjectivism is the theory that perception (or consciousness) is reality, and that there is no underlying, true reality that exists independent of perception. It does not, however, claim that "all is illusion" or that "there is no such thing as reality", merely that the nature of reality is dependent on the consciousness of the individual. In an extreme form, it may hold that the nature and existence of every object depends solely on someone's subjective awareness of it.

It is very similar to the doctrine of Solipsism and is related in some ways to metaphysical Relativism. The antithesis of Subjectivism is Objectivism, which holds that reality exists wholly independent of the mind. Another concept related to Subjectivism is that of Panpsychism, the view that all parts of matter involve mind, that everything is sentient and that there are either many separate minds, or one single mind that unites everything that is.

Metaphysical Subjectivism is the idea (as described above) there is no underlying, true reality that exists independent of perception or consciousness.

Ethical Subjectivism (or Moral Subjectivism) is the meta-ethical belief that ethical sentences reduce to factual statements about the attitudes and/or conventions of individual people, or that any ethical sentence implies an attitude held by someone. It is therefore a form of Moral Relativism in which the truth of moral claims is relative to the attitudes of individuals. The opposite position is that of Moral Objectivism or the more extreme Moral Absolutism.